This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In order to test a hypothesis about mobility of the iron-sulfur domain n this protein, we need to collect data from a crystal form in which this domain is trapped immobile by crystal contacts. This is the case in the P6522 crystals which we used previously (Zhang et al. Nature 1998 392: 677-84;also structure 1BE3 deposited by another group. Now we are trying to grow these crystals again and improve the resolution, but the home source is out of commission so we need to screen as well as collect at the synchrotron.